TIMBER RAmLESNAmS AND LOUISIANA PINE SNAKES OF THE WEST GULF COASTAL PLAIN: HYPOTHESES OF DECLINE

-Timber rattlesnakes (Crotalus horrid=) and Louisiana pine snakes (Pituophis melanoleucus ruthvenq are large-bodied snakes occurring on the West Gulf Coastal Plain. Both species are thought to be declining .due to increasing habitat alteration. Timber rattlesnakes occur in closed canopy hardwood and pine-hardwood forests, and Louisiana pine snakes in pine forests on sandy, well drained soils. While various factors are probably involved in population declines, this study examined one factor for each species that may have widespread consequences for population viability. Results obtained in this study support the premise that timber rattIesnakes are vulnerable to mortality associated with roads and vehicular traffic. Data and discussion are presented suggesting that populations are negatively impacted in areas of eastern Texas having a high road density. Conversely, Louisiana pine snakes appear to be affected by changes in the fire regime which has altered vegetation structure resulting in decreases in pocket gopher (Geomys breviceps) density. Decreases in gopher densities are further hypothesized to result in decrease or extirpation of pine snake populations. Timber rattlesnakes (Crotalus horridus) and Louisiana pine snakes (Pituophis rnelanoleucus ruthveni) are large-bodied snakes with low reproductive rates. Thus, they are vulnerable to population decreases due to habitat modifications and increased mortality rates. Anecdotal evidence suggests that both species are declining on the West Gulf Coastal Plain (Conant 1956; Young & Vandeventer 1988; Brown 199 1). Consequently, the Texas Parks and Wildlife Department has listed the timber rattlesnake as threatened and the Louisiana pine snake as endangered in Texas (TPWD 1992). In an effort to understand the biology of these two species and elucidate factors that are potentially responsible for the presumed population declines, radio-telemetry studies of both species were initiated. Both species are undoubtedly subject to a variety of human induced impacts that have reduced populations and resulted-in extirpation of local populations. However, this study focuses upon two hypotheses, one for each species, that the authors suspect are of importance in causing 112 THE TEXAS JOURNAL OF SCIENCE-VOL, 49(3) SUPPLEMENT, 1997 Table 1. Annual home range size (ha) of adult timber rattlesnakes in eastern Texas. Snake Minimum Convex Harmonic Mean Polygon 95% Contour TX 1 (male) 105.4 123.7 1993 TX 1 (male) 113.6 148.8 1994 TX 2 (male) 212.6 256.7 TX 3 (female) 19.5 22.1 TX 4 (female) 20.2 15.3 declines on a landscape level. Timber rattlesnake ecology. -Timber rattlesnakes on the Gulf Coastal Plain are typically associated with hardwood and mixed pine-hardwood forests (Martin 1992). Extensive areas dominated by longleaf pine (Pinus palustn's) are generally not occupied (Mount 1975; Dundee & Rossrnan 1989). This general pattern is consistent with observations made in eastern Texas during this study. Timber rattlesnakes are classic ambush predators, often spending up to several days in a given position waiting for prey to pass within striking distance. Foraging snakes frequently assume positions adjacent to logs, tree trunks or other structures that may be used as travel corridors by prey species (~einkrt et al. 1984; Brown & Greenberg 1992). Juveniles occasionally climb trees to heights of 15 rn, and may remain in trees for several days (Saenz et al. 1996). Prey typically consists of small mammals up to the size of squirrels (Sciums spp.) and rabbits (Silvulagus spp. ) (Klauber 1 956). Preliminary radio-telemetry results document the large home ranges of adult male timber rattlesnakes in eastern Texas (Table 1). Adult females have substantially smaller home ranges. The average annual home range size (Harmonic Mean 95% contour) for adult females (19 ha) is much smaller than that of adult maIes (176 ha). Juvenile snakes have generally smaller home ranges than adult females. The difference in home range size between -adult females and adult males is primarily due to differences in movement patterns associated with breeding activities. RUDOLPH & BURGDORF 113 Table 2. Average daily distance moved (rn) by adult male and fernale timber ragIesnakes during the mating and non-mating season.